Fracking into underground drinking water isn’t prohibited, but officials of the energy industry have said they don’t do it because oil and gas deposits lie far beneath aquifers, the Times reported.

The scientists' research doesn’t say that drinking water has in fact been contaminated, but that “thousands of gallons of diesel fuel and millions of gallons of fluids containing numerous inorganic and organic additives were injected directly into Wind River and Fort Union geological formations in Wyoming, which contain natural gas and drinking water sources.

“The extent and consequences of these activities are poorly documented, hindering assessments of potential resource damage and human exposure,” Dominic DiGiulio of Stanford’s School of Earth Sciences wrote in the report.

Fracking often occurs miles beneath the surface. But the study, which plotted the depths of fracked wells and drinking water wells in the Pavillion area, found fracking at the depths of the deepest water wells in the area: 700 to 750 feet.

The EPA doesn’t track fracking in water sources, the Times said. EPA studies during the past six years found evidence of contamination at sites in Pennsylvania, Texas, and Wyoming, but the investigations were shelved.

Tight geological formations are thought to protect water sources, but the scientists say the geological formations may not be as impenetrable as many think.

“We think that any fracking within a thousand feet of the surface should be more clearly documented and face greater scrutiny,” Robert Jackson of Stanford’s School of Earth Sciences said, according to the Times.

Fracking for oil and gas is occurring through some underground sources of drinking water, The Los Angeles Times reports, citing a Stanford University study released Tuesday that heightens concerns over the possibility of drinking water being contaminated with known carcinogens and neurotoxins.